The resin coated copper foil has been used for various applications in the field of manufacturing printed wiring boards. For example, Patent Document 1 discloses adopting of the resin coated copper foil without resin on a peripheral region to prevent generation of dents at the rear surface of a resin coated copper foil, and the construction of the resin coated copper foil is utilized for preventing of dents in hot pressing.
In addition, Patent Document 2 discloses a method for laminating a resin coated copper foil on an inner layer board for forming a build-up layer in a build-up process for printed wiring board. To finish a precise pattern accurately, target is set to prevent generation of dimples on the copper foil around IVHs in hot-pressing to perform reliable adhesion with a dry-film resist without bubbles. To achieve the object, resin coated copper foil having a requisite thickness of copper foil is used to minimize the level of dimple not to affect proccessability even the resin component comprising the resin coated copper foil flow into IVHs of the inner layer.
Alternatively, the resin coated copper foil has excellent migration resistance because of no inclusion of reinforcements in the resin layer. Same time, it has been used for the application which requires less weave pattern on the laminate which is caused when glass cloth in a per-preg as a reinforcement is used. For example, Patent Document 3 discloses the technology to prevent a wiring layer and wiring pattern from contact with the glass fiber provided in the glass fiber reinforced substrate by arranging an insulating film containing no glass fiber among a glass fiber reinforced substrate. As a result, even in the operation with a high voltage, risk of insulation failure between wiring layer and wiring pattern is prevented and cost increase to finish a printing wiring board etc. is minimized. More specifically, the printed wiring board disclosed is characterized in that the dielectric layer containing no glass fiber is made of an insulating resin portion of the resin coated copper foil, and the copper foil portion of the resin coated copper foil is made to be a copper foil layer where the wiring pattern is formed. The document discloses that migration resistance may be improved and adhesion among the insulating layer, the wiring layer and the wiring pattern may be improved as a result and high reliability and long shelf life can be achieved in the printed wiring board.
As is apparent from the descriptions above, the resin coated copper foil has been used for overcoming drawbacks of a printed wiring board caused by its construction.
The present applicant have been engaged in the invention disclosed in Patent Document 4 disclosing technology directing to the most suitable resin coated copper foil for the aforementioned applications. Technology disclosed in the Patent Document 4 is directing to provide halogen-free resin coated copper foil having excellent flame retardant property, excellent moisture resistance, heat resistance, and enough peel strength between a substrate and a copper foil, and employs halogen-free resin composition which is characterized by containing an epoxy resin comprising an epoxy resin curing agent which contains nitrogen in an amount of 5 to 25 wt %, a thermosetting maleimide compound, for forming a resin layer constituting resin coated copper foil.
Furthermore, the present applicant disclose the following technology in Patent Document 5 which is directing to provide resin coated copper foil for manufacturing a printed wiring board having properties well-balanced in flame retardant property, resin flowability, moisture resistance and peel strength. The technology discloses a resin coated copper foil comprising a resin layer on one side of copper foil and is characterized in that the resin layer is formed of a resin composition containing (a) a high-molecular weight polymer having an intermolecular crosslinkable functional group and a crosslinking agent thereof (5 to 30 parts by weight), (b) an epoxy resin which is liquid state at 25° C. (5 to 30 parts by weight) and (c) a compound having a structure represented by Formula 4 (40 to 90 parts by weight).

In the inventions disclosed in Patent Documents 4 and 5 mentioned above, finished printed wiring board performs excellent flame retardant property, excellent moisture resistance, heat resistance, etc. and enough peel strength between a substrate and copper foil, and offers performance over conventional resin coated copper foil. That is, the excellent moisture resistance referred to in the inventions disclosed in Patent Documents 4 and 5 is the moisture resistance of the fully-cured state of resin which constitutes resin coated copper foil.    [Patent Document 1] Japanese Patent Laid-Open No. 11-348177    [Patent Document 2] Japanese Patent Laid-Open No. 2001-24324    [Patent Document 3] Japanese Patent Laid-Open No. 2001-244589    [Patent Document 4] Japanese Patent Laid-Open No. 2002-179772    [Patent Document 5] Japanese Patent Laid-Open No. 2002-359444